DESCRIPTION (Investigator's Abstract): The goal of this study is to understand how neural circuitry in the brain generates the eye movements required to maintain gaze stability. This problem is of clinical importance since loss of gaze stability severely degrades visual acuity. Since the vestibuloocular reflex (VOR) serves as a model for motor system function in general, this project will also help to increase understanding of other critical motor processes such as limb movements, postural control and locomotion. A powerful new approach involving analysis of motor function in 3 dimensions will be used to examine properties of the VOR, optokinetic reflex and smooth pursuit response and of the neural pathways that mediate them. This approach has already led to characterization of the spatial transformations that take place in the VOR and vestibulo-collic reflex and has begun to reveal how these transformations are implemented at the neural level. We will now extend our analysis to additional classes of neurons, measuring their spatial and dynamic properties during rotation of an animal or of its visual surround in many planes in 3-dimensional space. The final goal is to determine precisely how the brain transforms vestibular input into muscle output. When normal 3-dimensional vestibuloocular behavior has been characterized, plastic changes in the VOR that follow visuo-vestibular training will be studied at reflex and neural levels. At the latter level, we will continue our pioneering efforts to study changes in neural responses during plastic, adaptive changes in the VOR. The overall goal is to understand how the nervous system compensates for lesions that affect vestibuloocular function, a problem of great importance in the care and rehabilitation of patients suffering from stroke, head trauma or other neurological problems. These experiments, which are based on new models of the plastic process, should also bring us closer to understanding the neuronal mechanisms underlying motor learning.